Embodiments of the present invention relate to the deposition of material in trenches formed in a substrate.
In the processing of integrated circuits and other electronic circuitry on a substrate, materials are deposited or otherwise formed on a substrate by, for example, chemical vapor deposition (CVD), physical vapor deposition (PVD), oxidation, nitridation, and ion implantation. In CVD processes, a deposition gas is used to deposit material on the substrate by heating or in a plasma. In PVD processes, a target is sputtered with an energized gas to deposit material on the substrate. In oxidation and nitridation processes, an oxide or nitride material, such as silicon dioxide or silicon nitride, is formed on the substrate by exposing the substrate to a suitable gaseous environment. In ion implantation, ions are implanted into the substrate. Thereafter, one or more of these materials may be etched to form features, such as trenches, which may be shaped as holes or channels. In the etching process, a pattern of etch-resistant features comprising resist, hard-mask, or both, are formed on the substrate and the exposed portions of the substrate between the etch-resistant features are etched to form the trenches. Thereafter, the trenches may be filled with additional materials for forming other features or layers on the substrate. Planarization processes may also be used to smooth out the surface topography of the substrate in between the deposition of multiple layers.
In such substrate processes, it is sometimes desirable to etch a shallow trench, for example, to form a gate, and subsequently, to fill the etched shallow trench with a dielectric material. An embodiment of a conventional deposition process for etching and filling shallow trenches 304 in a substrate 300 is illustrated in FIGS. 3a to 3c. Referring to FIG. 3a, a gate oxide layer 301 (typically silicon dioxide) and a silicon nitride layer 302 is sequentially formed on a substrate 300, such as a silicon wafer. The silicon nitride layer 302, gate oxide layer 301, and substrate 300, are then etched to form the shallow trenches 304. Thereafter, as shown in FIG. 3b, a liner oxide layer 305 is formed in the shallow trenches 304 and the trenches 304 are over-filled with an oxide layer 306 (also typically silicon dioxide). As shown in FIG. 3c, the portions of the oxide layer 306 that lie over the silicon nitride layer 302 may then be removed by chemical-mechanical polishing or etch-back processes.
In shallow trench isolation processes, it is often necessary to overfill the trenches to provide a sufficient thickness of oxide material overlying the trenches that subsequent planarization processes can planarize the substrate surface without causing remaining oxide to dish or otherwise form an uneven surface topography. Typically, the oxide material is deposited in the trenches by a sub atmospheric chemical vapor deposition process (SACVD) or by a high density plasma chemical vapor deposition process (HDPCVD). Both these processes result in an uneven surface topography. For example, FIG. 1 shows a typical uneven surface topography of a SACVD derived oxide layer 206 deposited to overfill the trenches 204. FIG. 2 shows a typical uneven surface topography of a HDPCVD oxide layer 406 deposited to overfill the trenches 404. The results of the over-filling processes are represented by reference numbers 207 and 407. Because of such uneven surface topographies, the oxide layers 206 and 406 should be deposited sufficiently thick to prevent the remaining oxide material from dishing or having a non-uniform surface, when the oxide layers 206 and 406 are partially removed in the subsequent planarization process. However, deposition of the relatively thick sacrificial oxide layer undesirably increases the cost of the overall deposition process while reducing process throughput.
Thus, it is desirable to be able to reduce the costs of trench filling processes, especially for filling shallow trenches. It is further desirable to improve the overall speed of the deposition process and increase process throughput. It is also desirable to be able to deposit high quality oxide material in the trenches. It is also desirable to be able to deposit a relatively thick oxide layer on the substrate to reduce formation of dishing or uneven surface topographies in subsequent planarization processes.
A method of filling a trench in a substrate having a gate oxide layer and an overlying silicon nitride layer, the method comprising, in a first deposition process, exposing the substrate to a first gas maintained at process conditions that cause the first gas to deposit in the trench in the substrate, a first silicon oxide material having a first lower shrinkage; and in a second deposition process, exposing the substrate to a second gas maintained at process conditions that cause the second gas to deposit in the trench, a second silicon oxide material having a second higher shrinkage.
In another aspect, a substrate processing method comprises providing a substrate, forming a gate oxide layer on the substrate, depositing a silicon nitride layer over the gate oxide layer, etching the silicon nitride layer, gate oxide layer, and the substrate, to form the trench in the substrate; in a first deposition process, depositing a first silicon oxide material in the trench in the substrate, the first silicon oxide material having a first shrinkage; and in a second deposition process, depositing a second silicon oxide material in the trench to overfill the trench, the second silicon oxide material having a second shrinkage that higher than the first shrinkage; and planarizing the substrate.